Recently, for example, portable telephones, PDA (Personal Digital Assistant) terminals, and many other electronic devices comprises a plurality of printed wiring boards, which are applied with printed wires and mounted with a lot of electronic parts, and which are contained in a limited volume of electronic devices. Then, with an increasing reduction in thickness and volume, a variety of technologies have been disclosed as method of laminating a plurality of these printed wiring boards and holding them in connection with each other, in order to realize a reduction in size of printed wiring boards.
FIG. 1 is a schematic cross-sectional view showing the structure of connections in a printed board disclosed in JP-8-96870-A. According to the technology described in detail in this figure, first printed board 1304, second printed board 1305, and third printed board 1306 are laminated on first resilient member 1303 embedded in base 1301, while being positioned by guide rod members 1302 disposed on base 1301. Then, intermediate plate member 1307 is fixed to base 1301 with screws from above them. Further, fourth printed board 1308, fifth printed board 1309, and sixth printed board 1310 are laminated from above intermediate plate member 1307 while being positioned by guide rod members 1302. Resilient members 1311 are disposed from above sixth printed board 1310 at sites corresponding to portions of these printed boards which have conductive patterns, and board keep plate 1312 is fixed to intermediate plate member 1307 by screws from above resilient member 1311. In this way, first printed board 1304, second printed board 1305, and third printed board 1306 are connected by the impact resilient force of resilient member 1303 and resilient member 1311 with their conductive patterns brought into contact with each other. Likewise, fourth printed board 1308, fifth printed board 1309, and sixth printed board 1310 are connected by the impact resilient force of resilient member 1303 and resilient member 1311 with their conductive patterns brought into contact with each other.
FIG. 2 in turn is a schematic cross-sectional view showing the structure of connections in a printed board disclosed in JP-8-307030-A. According to the technology described in detail in this figure, rigid board base 1405 is mounted with one-side flexible printed board (FPC: Flexible Printed Circuit) 1401 formed with conductor 1402 on a surface thereof, and two-side FPC 1403 is laminated thereon, with conductor 1404 formed on a back surface and conductor 1409 is formed on a front surface. Anisotropically conductive rubber 1406, which is a resilient member, is disposed from above two-side FPC 1403 at sites corresponding to portions of these printed boards which have conductive patterns. Further, rigid one-side hard board (PWB: Printed Wire Board) 1407 is laminated from above anisotropically conductive rubber 1406 with conductor 1410 formed on a back surface thereof. This one-side PWB 1407 is secured to board base 1405 with fastening of screws 1408 to apply uniform pressure to the entireties of these wiring boards, thereby sufficiently crushing anisotropically conductive rubber 1406 to develop conductivity. In this way, conductor 1402 formed on the front surface of one-side FPC 1401 is electrically connected to conductor 1404 formed on the back surface of two-side FPC 1403, and conductor 1409 formed on the top surface of two-side FPC 1403 is electrically connected to conductor 1410 formed on the back surface of one-side PWB 1407.
FIG. 3 in turn is a schematic exploded perspective view showing a method of pressure connecting flexible circuit boards, disclosed in JP-2001-244592-A. According to the technology described in detail in this figure, mount 1501 is provided on a body base, and mount 1501 is formed with recess 1501a in a central region thereof. Pressure connection rubber 1502 is attached to this recess 1501a. Flexible circuit boards 1503, 1504, 1505, and tongue piece 1506 formed on flexible circuit board 1503 are laminated from above them, and are positioned to the body base through pins 1507a and 1507b formed on mount 1501. Pressure connection fixture 1508 formed with a protrusion is attached by screw member 1509 with the protrusion facing pressure connection rubber 1502, thereby electrically connecting contact patterns formed on laminated flexible circuit boards 1503, 1504, and 1505 as well as tongue piece 1506, respectively, to be in contact with each other, with the resilient force of resiliently deformed pressure connection rubber 1502 and with the pressure of pressure connection fixture 1508 applied to the protrusion.
FIG. 4 in turn is a schematic cross-sectional view showing the structure of a connection using an electric connector, disclosed in JP-2002-8749-A. According to the technology described in detail in this figure, on metal made back-up plate 1601 having a positioning pin 1603 implanted thereon, mounting circuit board 1604 is positioned and horizontally mounted. Mounting circuit board 1604 has an outside shape larger than back-up plate 1601, and comprises a plurality of electrodes 1605 arranged in a matrix in a central region of a surface of its own. On the top, matching plate 1608 is laminated. Rectangular opening 1609 is formed at the center of this matching plate 1608, and contains insulating resilient sheet 1613 which is formed with electric connector 1612 and which has a thickness larger than the thickness of matching plate 1608 by 0.05 to 0.1 mm.
Electric connector 1612 comprises a plurality of resiliently deformable resilient connection pins 1614 which are arranged on a surface of resilient sheet 1613 and which protrude in the direction in which semiconductor package 1630 is mounted. Each resilient connection pin 1614 contains a plurality of metal ribbons 1615, both ends of which protrude or are exposed. From above this, positioning plate 1617 is laminated, and from above this, positioning holder 1621 having opening 1622 is laminated. Then, positioning holder 1621, positioning plate 1617, matching plate 1608, mounting circuit board 1604, and back-up plate 1601 are integrated by screwing a plurality of bolts into them. Subsequently, semiconductor package 1630 having a plurality of electrodes 1631 formed on a back surface thereof is contained and compressed in opening 1622. In this way, resilient sheet 1613 of electric connector 1612 is compressed and deformed, causing mounting circuit board 1604 and semiconductor package 1630, opposing each other, to be electrically connected.
FIG. 5 in turn is a schematic cross-sectional view showing the applied product of an anisotropically conductive connector disclosed in JP-2003-77559-A. According to the detailed description of the applied product of the anisotropically conductive connector disclosed in this figure, anisotropically conductive connector 1702 is placed on circuit board 1755 such that conductor 1722 of resilient anisotropically conductive film 1720 is located on electrode 1756 of circuit board 1755. On this anisotropically conductive connector 1702, electronic part 1750 is placed such that its electrode 1751 is located on conductor 1722 on resilient anisotropically conductive film 1720 of anisotropically conductive connector 1702. Anisotropically conductive connector 1702 comprises frame plate 1710 having an opening formed at the center thereof, and resilient anisotropically conductive film 1720 having conductivity in a thickness direction is placed in this opening while it is supported by the edge of the opening of frame plate 1710. Also, frame plate 10 is formed with a plurality of positioning holes 1716 around its peripheral edge.
Resilient anisotropically conductive film 1720 comprises a functional area which includes a plurality of conductors 1722 which are arranged in accordance with a pattern corresponding to the pattern of electrode 1751 of electronic part 1750 and which extend in the thickness direction, and insulators 1723 formed around each conductor 1722 to insulate each conductor 1722 from one another. This functional area is placed such that it is located in the opening of frame plate 1710. Around the peripheral edge of this functional area, a supported area securely supported by the edge of the opening in frame plate 1710 is formed continuously to the functional area.
As described above, circuit board 1755, anisotropically conductive connector 1702, and electronic part 1750 are laminated. Then, from above this, a leg of fixing member 1752 is inserted through positioning hole 1716 and positioning hole 1757 formed through circuit board 1755, and electronic part 1750 and anisotropically conductive connector 1702 are fixed on circuit board 1755 such that conductor 1722 on resilient anisotropically conductive film 1720 is sandwiched between electrode 1751 of electronic part 1750 and electrode 1756 of circuit board 1755. In this way, conductor 1722 of resilient anisotropically conductive film 1720 develops conductivity, causing electrode 1751 of electronic part 1750 to be electrically connected to electrode 1756 of circuit board 1755.
However, the foregoing conventional technologies imply the following problems. In the technology disclosed in JP-8-96870, the connection of the printed boards with each other is made through contacts of the conductive pattern with each other, and this contact pressure is generated only by the resilient force of the resilient members disposed on the topmost and lowermost layers of the circuit board device. For this reason, the contact area is not consistent due to variations in the shape of terminals of the conductor pattern, particularly, the thickness, area and the like thereof, resulting in an instable electric resistance.
Also, when the printed wiring board deforms due to an external force or the like, the structure is not such that the deformation of the printed wiring board is not transmitted to the resilient members. Thus, the resilient members also deform in association with the deformation of the printed wiring board, resulting in fluctuations in resilient force, i.e., contact pressure and a consequently instable electric resistance.
Further, since the circuit board device is structured such that the base which is embedded with the resilient member and the base keep plate are disposed on the topmost and lowermost layers thereof, it is difficult to realize compactization associated with a reduction in thickness and volume of an electronic device which has this structure. Further, since the connection structure of a plurality of printed wiring boards is electrically disrupted by a plurality of connect layers with the intermediate plate member sandwiched therebetween, a separate connection structure is required for electrically connecting a plurality of these connect layers with each other. In particular, when an increased number of printed wiring boards is to be laminated, it is difficult to realize the compactization associated with a reduction in thickness and volume of an electronic device which has this structure.
On the other hand, in the technology disclosed in JP-8-307030-A, a plurality of printed wiring boards are connected to each other by combining the contacts of the conductive patterns with each other, making use of the resilient force of the anisotropically conductive rubber with the contacts of the conductive patterns that make use of the pressing force of one-side of the hard board. As such, the contact area is not consistent due to variations in the shape of terminals of the conductive patterns in the contact connections, particularly, the thickness, area and the like, resulting in instable electric resistance. In particular, when a plurality of layers of contact connections are provided, the variations are multiplied, causing the electric resistance to be further instable.
Also, when the printed wiring board deforms due to an external force or the like, the structure is not such that the deformation of the printed wiring board is not transmitted to the anisotropically conductive rubbers. Thus, the anisotropically conductive rubbers also deform in association with the deformation of the printed wiring board, resulting in fluctuations in resilient force, i.e., contact pressure, a consequently instable electric resistance, and a possible break.
Further, in a region in which the printed wiring boards are connected to each other by making use of the resilient force of the anisotropically conductive rubber, a large shift appears between the connections of the printed wiring boards and the anisotropically conductive rubber due to the difference in the coefficient of linear expansion between the printed wiring boards and the anisotropically conductive rubber, resulting in an instable electric resistance and possible failures such as signal shorting or break. This problem can arise when the ambient temperature changes between −40° C. and 80° C., which is the storage temperature guaranteed range, required for small electronic devices such as portable telephones in particular.
On the other hand, in the technology disclosed in JP-2001-244592-A, a plurality of printed wiring boards are connected to each other through contacts in the conductive patterns that are in contact with each other, by making use of the resilient force of the pressure connection rubbers. For this reason, the contact area is not consistent due to variations in the shape of terminals of the conductive patterns in the contact connections, particularly, the thickness, area and the like, resulting in an instable electric resistance. In particular, when a plurality of layers of contact connections are provided, the variations are multiplied, causing the electric resistance to be further instable.
Also, when the printed wiring board deforms due to an external force or the like, the structure is not such that the deformation of the printed wiring board is not transmitted to the pressure connection rubber. Thus, the pressure connection rubber also deforms in association with the deformation of the printed wiring board, resulting in fluctuations in resilient force, i.e., contact pressure, a consequently instable electric resistance, and a possible break.
Also, when an increased number of printed wiring boards is to be laminated, the connection pressure rubber must be increased in hardness, or the connection pressure rubber must be increased in size to increase the resilient force, in order to generate a larger pressure force for ensuring electric connection through the contacts of the conductive patterns that are in contact with each other. Accordingly, it is difficult to realize the compactization associated with a reduction in thickness and volume of an electronic device which has this structure.
On the other hand, in the technology disclosed in JP-2002-8749-A, the mounting circuit board and semiconductor package are connected by making use of the resilient force of the resilient connection pins and the metal ribbons embedded in the resilient connection pins. This is not a structure which prevents deformations of the mounting circuit board and semiconductor package from being transmitted to the resilient connection pins if the mounting circuit board and semiconductor package deform due to an external force or the like. Thus, the resilient connection pins also deform in association with the deformation of the mounting circuit board and semiconductor package, resulting in fluctuations in resilient force, i.e., contact pressure, a consequently instable electric resistance, and a possible break.
On the other hand, in the technology disclosed in JP-2003-77559-A, the electrode of the circuit board is connected to the electrode of the electronic part by sandwiching the resilient anisotropically conductive film supported by the edge of the opening of the frame plate. For this reason, when the resilient anisotropically conductive film is sandwiched, a repellent force is generated by this resilient anisotropically conductive film, so that the thickness in the laminating direction must be increased in order to prevent deformations due to this repellent force. In other words, it is difficult to realize the compactization associated with a reduction in thickness and volume of an electronic device which has this structure.